The present invention relates to caged female threaded fasteners which provide high torsional strength while allowing removal of the fasteners for servicing.
It is a common manufacturing practice to apply coatings of paint or other decorative or protective coatings to large subassemblies prior to final assembly of the completed product. For example, in the manufacture of automobiles, the body of the automobile will be formed and assembled, and then painted. Other automotive subassemblies, such as suspension parts, undercarriages, or closures for the automobile (such as the doors, hood, and trunk lid) are separately manufactured and painted, and are assembled with the painted automobile body to form a complete automobile.
In most cases, the subassemblies of the automobile will be secured to the auto body by threaded fasteners. However, the use of threaded fasteners often presents difficulties in final assembly. For example, in the case of assembling a door into a body, one of the matching threaded fasteners, for example, a female fastener, may be located inside a door pillar. The door pillar in a modern automobile of unibody construction very often is a hollow metal part which may be completely enclosed after manufacture of the vehicle body. In order to provide a female fastener inside the pillar, it is necessary to mount the female fastener, for example by welding, inside the pillar when the body is being manufactured.
Due to variations in manufacturing tolerances, a degree of position adjustment for the female fastener must be provided so that the door and body may be properly aligned during final assembly. Position adjustment is provided by using a female fastener called a xe2x80x9ccage-nutxe2x80x9d, which is usually a nut encaged in a structure that is attached to the inside of the door pillar. The nut is provided with a range of movement within the encaging structure so that when the door is assembled to the body, the alignment of the door and the body can be adjusted until they meet manufacturing standards.
Cage-nuts are also frequently used in situations where the nut is not completely enclosed, such as on the frame of the vehicle. In these situations, the use of a cage-nut welded onto the body prior to final assembly reduces the time needed for final assembly of the automobile.
It has been found, however, that during the step of painting and baking paint on the body of the auto, that the nut will often weld or adhere to the cage. This paint-welding creates problems in the step of assembling and aligning the door or other subassembly within the body, because the nut no longer has any freedom of movement. It can be difficult to free the paint welded nut from the cage if it is in an enclosed space. Consequently, the final assembly of the automobile will be slowed while these parts are freed up enough so that the door or other subassembly can be properly aligned and assembled with the body.
Another problem associated with such cage-nut assemblies is that a bolt may be stripped or cross-threaded into the encaged nut, particularly if the nut is misaligned as a result of adhering to the cage structure. In this situation, it is difficult, if not impossible, to remove the nut and bolt for servicing because the nut may not be removable from the cage. Accordingly, it is desirable to provide an improved cage-nut design in which the frequency of paint-welding the nut to the cage structure is minimized, and the nut is removable from the cage for servicing when the bolt or nut are stripped or cross-threaded.
The present invention overcomes the above referenced shortcomings of prior art cage-nut assemblies by providing a cage-nut assembly including a Teflon-coated nut and a cage structure which provides high torsional strength while providing a structurally weak portion which allows bending of the cage structure for removal of the nut for servicing.
In a first embodiment, a flat base is provided with opposing strap portions which wrap around opposing ends of an oblong (i.e., longer than wide, including diamond shape or other shape providing a portion for containment and torsional resistance), Teflon-coated nut. The flat base forms an enclosed aperture for receiving a bolt. The straps are bendable away from the body to facilitate nut removal. The straps are configured to provide high torsional strength. Small tabs extend from the base to space the nut away from the base to prevent paint-welding of the nut to the base, and are bendable to allow the nut member to seat when torqued down.
In another embodiment, standoff legs support a flat base with an enclosed aperture formed therethrough for receiving a bolt. A rectangular Teflon-coated nut is positioned within the cage. The legs include small, bendable tabs which hold the nut in position and are bendable to allow the nut member to seat when torqued down (when a bending-force of approximately 65 lbs. is applied to the legs). One of the tabs prevents the nut from sliding out of the cage, and is bendable to allow removal and servicing of the nut (when a bending-force of approximately 10 to 20 lbs. is applied).
In a further embodiment, the cage-nut assembly includes a nut positioned within a cage structure, the cage structure being configured to provide high torsional strength to prevent rotation of the nut. Preferably, the cage structure provides sufficiently high torsional strength that the first failure would be that of the weld holding the cage structure against a workpiece when a significant torque is applied to the nut (preferably at approximately 190 Nm). The cage structure has a flat base and an at least partially open end portion. The cage structure includes a relatively structurally weak blocking member preventing the nut from exiting the cage structure through the end portion. The structurally weak blocking member is bendable when less than approximately 20 lbs. of force is applied to the blocking member to open the end portion and allow the nut to move laterally along the base through the end portion for removal of the nut. The flat base includes a bolt-receiving aperture which is formed coextensively with the at least partially open end portion. The blocking member comprises first and second curved tangs formed coplanar with the flat base. The nut includes a protruding tubular portion which extends through the bolt-receiving aperture. Standoff legs support the flat base and include small projections to facilitate projection welding.
In the various embodiments, the flat base may be positioned flat against a workpiece to which the nut is being attached, or may be spaced from the workpiece by the above-described standoff legs.
Accordingly, an object of the invention is to provide an improved cage-nut assembly in which the nut is removable from the cage for servicing.